Depo-Provera, also known as medroxyprogesterone acetate, is a highly effective form of birth control that contains synthetic progesterone. Given every 3 months as an injection into the patient's muscle, this contraceptive works by preventing the release of an egg (ovulation) and by making it difficult for a fertilized egg to implant in the woman's uterine wall. One of the most common side effects of Depo-Provera is irregular menstrual bleeding. Women taking Depo-Provera may notice that they have longer or shorter than normal menstrual periods or that their periods are heavier or lighter than normal. Some women may also find that their menstrual periods start earlier or later than expected. During the first few months of Depo-Provera use, women will likely also notice irregular bleeding or spotting between menstrual periods. To deal with irregular periods, women on Depo-Provera should always have feminine protection with them at all times in case unexpected bleeding occurs. If a woman experiences very heavy or prolonged bleeding while taking Depo-Provera, she may want to contact her doctor for guidance.